The Avidin-Biotin-Peroxidase Complex enzyme-linked immunosorbent assay (ABC-ELISA) with antigen from gerbils infected with alveolar hydatid (GAH) was performed on the sera of 54 patients with multilocular echinococcosis, 107 patients with other diseases and 102 healthy adults. All the sera were diluted 1:200 and an S/N value greater than 2.2 was taken as positive. Both the sensitivity and specificity were 98.1%. The S/N value (mean +/- SD) of sera of the patients with multilocular echinococcosis, other parasitic diseases, tuberculosis, other diseases and healthy adults were: 5.9 +/- 3.0, 1.1 +/- 0.4, 1.4 +/- 0.8, 1.1 +/- 0.5 and 1.0 +/- 0.4. The geometric mean titre (GMT) of antibody measured by ABC-ELISA was 13.7 times that of ELISA. The quantity of serum used in ELISA was 8 times that of ABC-ELISA. ABC-ELISA might be particularly helpful to identify cases with low immune responsiveness. In the detection of alveolar hydatidosis and cystic disease with GAH antigens, the positivity was 98.1 and 67.1% with 87 and 25.6% having S/N greater than 5, respectively. It is suggested that in the diagnosis of hydatid diseases by ABC-ELISA, homologous antigen should be used. The temperature and the incubation time needed for the present assay are practical, for the total time requires only 55 minutes.